A textile product of this kind is known, for example, from U.S. Pat. No. 6,158,576. The known textile product comprises in its matrix a sensor that is excited by means of Nd:YAG laser radiation and as a result emits radiation having a wavelength different from the excitation wavelength. This radiation is detected by means of a detector in the vicinity of the textile product, thus making it possible, by means of the intensity and amplitude of the wavelength of the radiation emitted by the sensor, to ascertain information such as, for example, the speed or temperature of the textile product.
A principal disadvantage of this arrangement may be seen in the fact that the individual components, such as the Nd:YAG laser, detector, and analysis computer, are very cost-intensive. In addition, the individual components require a great deal of space, and their arrangement with respect to one another is relatively inflexible. Measurement can thus be performed only at specific measurement points, so that certain regions of the textile product cannot be reached by the specified measurement arrangement.
The document WO 93/21378 discloses a non-contact measurement method by induction. An electrically conductive or magnetizable metal strip is woven for this purpose into the textile product. Measurement serves to define the position of the textile product in the paper machine, and is accomplished by means of two detectors between which the textile product passes.
The disadvantage of a limited number of measurement points and the inaccessibility of specific process regions exists here as well. In addition, only positioning errors of the textile product in the paper machine can be detected by means of this measurement assemblage. It is not possible to measure the speed, pressure, or temperature of the textile product.
The document DE 43 11 402 A1 discloses a measurement apparatus, arranged outside a paper machine felt, for measuring the temperature and water permeability of the paper machine felt. The measurement apparatus comprises, for that purpose, a microwave head that is connected to a vacuum source. The measurement head is placed onto the felt, and the felt is aspirated against the measurement head by means of a vacuum source. A temperature transducer in the measurement head measures the temperature of the air and water that are sucked in. At the same time, the quantity of water pulled out of the felt is determined by means of a microwave radiator located in the measurement head. The temperature measurement allows uniform propagation of the press section's dewatering energy over the web, and also over the felt, to be tracked.
The disadvantage of this measurement apparatus is on the one hand that the measurement head must be placed onto the textile product or paper machine felt. On the other hand, the configuration of the measurement head, with a microwave radiator to measure the quantity of water in the felt and a temperature sensor to measure the temperature of the air sucked through the measurement head into the air conduit, is very complex and cost-intensive. The number of measurement points is moreover limited, both in structural terms and for cost reasons.